Stud for stud welding

ABSTRACT

A welding stud includes a shank and a head flange, which projects radially relative to the shank and whose outer circumference is of polygonal design in order to be able to apply a test torque (T) to the stud by means of a tool. The flange includes an annular section ( 16 ) whose front facing and radially extending annular surface is designed as a welding surface. The annular section directly adjoins the flange, and the annular section and the flange form a head section which has a uniform outside diameter (D) throughout, and wherein the polygonal shape of the flange extends over the annular section up to its front annular surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application No.PCT/US2009/050047, filed Jul. 9, 2009 which claims the benefit of GermanApplication No. 10 2008 033 373.5, filed on Jul. 9, 2008, the disclosureof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a stud for stud welding, having ashank, having an axially adjoining flange which projects radiallyrelative to the shank, and having an annular section which axiallyadjoins the flange and whose front, radially extending annular surfaceis designed as a welding surface which is to be welded to a workpiece.

The invention also relates to a fastening arrangement having a workpieceand a stud welded to the workpiece and also relates to a method ofwelding a stud to a workpiece and to the use of such a stud for weldingonto a workpiece.

The invention generally concerns the field of stud welding. This weldingprocess is used, inter alia, to a great extent in the field of vehicletechnology. In this case, studs are welded to body sheets and serve asanchors for plastic fastening elements (clips), dashboards, etc.

The trend in recent years is to reduce the thickness of the body sheetsin order to reduce, for example, the weight of the vehicle. The weldingof studs onto body sheets that are becoming increasingly thinner turnsout to be difficult. As a rule, the studs have a conically taperingwelding surface. In order to fuse this surface during the stud welding,a relatively high input of energy is required. This may lead to“burn-through” of the body sheet.

Consequently, a welding stud which has a concave recess and is designedfor capacitor discharge welding has been proposed in document U.S. Pat.No. 3,671,710. In this case, the recess together with the outsidediameter of the stud results in an annular flange. This is intended toimprove the uniformity of the molten pool.

Document DE 196 11 711 A1 discloses a welding element having an annularflange structure. The annular flange has a margin narrowing in crosssection, such that an approximately linear edge is obtained at the frontend of the stud. The welding edge is set down on the workpiece. The studis then pulled back for forming an arc. Finally, the stud is pushed intothe complete molten pool. An approximately annular welding spot resultsoverall, and a cavity is formed between the stud and the workpiece inthe interior of this annular welding spot. It is mentioned that theconfiguration of the stud is intended to permit welding of the stud torelatively thin sheets by means of the drawn-arc process.

Finally, document WO 2004/033923 A1 discloses a fastening element inwhich a stud is welded onto a sheet (in particular a sandwich sheet).The stud has a region which serves as a predetermined breaking point inorder to achieve a defined failure case. A nut is screwed onto the stud,and the strength of the stud is adapted to the strength of the nut, suchthat the nut breaks first before the stud breaks. Provided the nut doesnot break, the stud breaks before the stud is torn out of the sheet.

In other words, a torque is not applied to the stud until during theassembly when a plastic fastening element or the like is actually putonto the stud. If a defect affecting the stud and/or the sheet occurs atthis moment for certain reasons, relatively expensive rework isnecessary. For at this moment the sheet is already painted as a rule andthe repair of the welding spot and the re-application of a studconsequently require complicated subsequent treatment of the surface ofthe body sheet.

The stud used has a shank, a flange section and an axially adjoiningannular section which together form a head section. The ratio of axiallength of the annular section to axial length of the head section (whichis formed by the flange and the annular section) is to be less than 50%,in particular within the range of 25% to 35%. Considerable importance isalso attached to other dimensions or ratios of dimensions of the headsection in this application. The outside diameter of the head section isdesigned to be round in this case.

Against the above background, an object of the invention is to specify acost-effective stud, an improved fastening arrangement and an improvedmethod of welding a stud onto a workpiece, wherein the workpiece has asmall thickness and wherein a situation in which expensive rework has tobe carried out in the assembly area in the event of failure of a weldedjoint can be avoided.

BRIEF SUMMARY OF THE INVENTION

This object is firstly achieved by a stud for stud welding, having ashank, having an axially adjoining flange which projects radiallyrelative to the shank and whose outer circumference is of polygonaldesign in order to be able to apply a test torque to the stud by meansof a tool, and having an annular section which axially adjoins theflange and whose front, radially extending annular surface is designedas a welding surface which is to be welded to a workpiece, wherein theannular section directly adjoins the flange, and the annular section andthe flange form a head section which has a uniform outside diameterthroughout, and wherein the polygonal shape of the flange extends overthe annular section up to its front annular surface.

The above object is also achieved by a fastening arrangement having aworkpiece and a stud of the type according to the invention welded tothe workpiece, wherein the workpiece has a thickness of less than 1 mm,in particular less than 0.8 mm.

The above object is also achieved by a method of welding a stud to aworkpiece and of checking the strength of the welded joint, comprisingthe steps:

providing a stud of the type according to the invention;

welding the stud onto the workpiece, in particular by drawn-arc studwelding; and

attaching a tool to the head section of the stud and applying apredetermined torque to the stud in order to check the strength of thewelded joint.

Finally, the above object is achieved by the use of a stud according tothe invention for welding onto a workpiece, the thickness of which isless than 1 mm, in particular less than 0.8 mm.

The stud according to the invention is suitable in particular forwelding onto very thin workpieces, such as thin body sheets. There hasbeen a trend in recent years for sheets of less than 1 mm, in particularless than 0.8 mm or even 0.6 mm and smaller. Due to the design of theannular section and of a welding surface formed as an annular surface,welding can be carried out in this case with a relatively small input ofenergy, such that the risk of burn-through of the sheet is reduced. Dueto the design of the polygonal shape at the outside diameter of the headsection, it is possible to check the strength of the welded joint. Thisis preferably done during the body-in-white phase, that is to say, forexample, immediately after the stud has been welded onto the workpiece.Consequently, any possible defective welded joint can be repaired ingood time. Expensive rework, as would be necessary in the event of arepair during the assembly phase, is not necessary. Furthermore, it hassurprisingly been found that, despite the polygonal shape throughout(which extends over the annular section up to front annular surface),essentially no disadvantages arise during the forming of the arc.Furthermore, the stud can be produced cost-effectively on account of thepolygonal shape throughout at the head section.

The object is therefore completely achieved.

It is especially preferred if the stud is made in one piece of metal, inparticular steel.

However, the stud can generally also be made of another metal, such asaluminum for example.

Furthermore, it is advantageous if the stud is produced by a coldforming process, in particular in a one-stage process with relativelylittle forming. This makes it possible for the shape of the stud to beof relatively simple design and for the polygonal shape to extend overthe entire outer circumference of the head section. In the case oflarge-flange studs, a multi-stage forming process may also be used. Evenin the case of a multi-stage process, the polygonal shape can beproduced by forming. This may be done, for example, by the larger flangebeing upset and deburred. The final shape is then formed in anadditional press stage using a press tool.

The shank may be of cylindrical design but preferably has a thread. Thethread may be a metric thread but is in particular a coarse thread.

The polygonal shape is preferably an octagonal shape.

In this embodiment, the stud can be produced cost-effectively.Furthermore, a comparatively simple tool can be used in order to exert atest torque on the already welded-on stud. However, the polygonal shapemay also be a hexagonal shape or another polygonal shape. Furthermore,the expression “polygonal shape” in this case is also intended to referto the fact that the outer circumference is toothed or has another shapediffering from a circular shape.

It is especially preferred if the ratio of the axial length of the headsection to the outside diameter of the head section is within the rangeof 1/7 to 3/4, in particular within the range of 1/3 to 3/4 in the caseof standard studs or 1/6 to 1/2 the case of large-flange studs.

In this way, the axial length of the head section can be designed to berelatively large, such that it is comparatively simple to attach a toolfor exerting a test torque.

According to a further preferred embodiment, the ratio of the axiallength of the flange to the axial length of the head section is withinthe range of 3/10 to 5/10.

In this way, the annular section can be designed to be relatively longin relation to the flange. Therefore firstly weight can be saved.Secondly the head section overall can have a comparatively small axiallength, such that a low overall height is obtained.

This applies in particular if the ratio of the axial length of theflange to the axial length of the head section is less than 5/10.

In the case of large-flange studs, the ratio of the axial length of theflange to the axial length of the head section is as a rule markedlybelow 5/10.

In the case of studs having a large flange diameter, it is advantageousto provide a locating point for automatic feeding into weldinginstallations and for the assembly (screwing on or mountingattachments). Said locating point is provided on the shank end faceopposite the head section and has a smaller diameter than the shank.

Furthermore, large-flange studs can also be provided pre-completed withplastic parts (plastic nuts, plastic components, etc.) or metal parts(cap nuts, flange nuts for ground studs or metal components) and bewelded automatically or manually.

It goes without saying that the abovementioned features and the featuresstill to be explained below can be used not only in the respectivelyspecified combination but rather also in other combinations or on theirown without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Exemplary embodiments of the invention are shown in the drawing anddescribed in more detail below. In the drawing:

FIG. 1 shows a partly sectioned side view of a stud according to anembodiment of the invention;

FIG. 2 shows a view of the stud of FIG. 1 from the front; and

FIG. 3 shows a fastening arrangement with a workpiece and a studaccording to FIGS. 1 and 2 welded onto the workpiece.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

An embodiment of a stud according to the invention is designatedgenerally by 10 in FIGS. 1 and 2.

The stud 10 has a shank 12, adjoining which in the axial direction is aflange 14. Adjoining the flange 14 in the axial direction is an annularsection 16, within which a recess 17 of circular cross section islocated.

A longitudinal axis of the stud 10 is shown at 18.

A front annular surface 19 is formed on the front end of the annularsection 16. The recess 17 extends from the front annular surface 19 upto the flange 14.

On the whole, the flange 14 and the annular section 16 form a headsection 20, the outer circumference of which has a polygonal shape 22,in the present case an octagonal shape.

A coarse thread 24 is formed on the shank 12. The stud 10 has an overalllength L. The axial length of the head section 20 is designated by K inFIG. 1. The axial length of the flange section is designated by F inFIG. 1. An outside diameter of the head section 20 is designated by D,and an inside diameter of the recess 17 is designated by A.

The ratio of the axial length F of the flange 14 to the axial length Kof the head section 20 is within the range of 3/10 to 5/10, in thepresent case approximately within the range of 4.5/10.

The ratio of the inside diameter A of the recess 17 to the outsidediameter D of the head section 20 is within the range of 5/10 to 8/10,preferably within the range of 6/10 to 7/10 .

The ratio of the axial length K of the head section 20 to the overalllength L of the stud 10 is within the range of 1/10 to 4/10, preferablywithin the range of 1.5/10 to 3/10. In the present case the ratio isabout 2/10.

The front annular surface 19 extends in the radial direction. The innercircumference of the annular section 16 is of circular design in crosssection.

FIG. 3 shows a fastening arrangement 30 according to the invention, saidfastening arrangement 30 having a stud 10 of the type shown in FIGS. 1and 2, said stud 10 being welded onto a workpiece 32. The workpiece 32is a metal sheet, preferably made of the same material as the stud 10 orof a material similar to that of the stud 10. The workpiece 32 has athickness W which is less than 1.0 mm, in particular less than 0.8 mm.In the present case the thickness W is about 0.6 mm.

As indicated schematically in FIG. 3, the stud 10 is suitable for fixinga plastic fastening element or clip 34, as is known per se in the priorart. The clip 34 may contain, for example, a receptacle 36 for acomponent 38. The component 38 may be, for example, a cable or a cableharness, a brake line or a fuel line.

In this case, the clip 34 bears on that side of the flange 14 whichpoints toward the shank 12, as shown in FIG. 3.

In the field of vehicle technology, the clip 34 is fastened to the stud10 as a rule in an “assembly area”. In this case, the body shell of thevehicle is produced and the workpiece 32 including the stud 10 is as arule already painted, such that the requisite attachments can be carriedout. The stud 10 is welded onto the workpiece 32 beforehand in a“body-in-white phase”.

Directly after the body-in-white phase and before further processingsteps, it is preferably checked whether the welded joint between thestud 10 and the workpiece 32 has sufficient strength.

In this case, during the body-in-white phase or before the assemblyphase, a torque T is exerted on the stud 10 about the longitudinal axis18 by means of a tool 40 (indicated schematically in FIG. 3). In theprocess, the tool 40 acts on the head section 20 provided with thepolygonal shape. The torque T that is applied in this case is apredetermined torque which a stud 10 correctly welded to the workpiece32 can absorb without damaging the welded joint and/or the stud 10.

In addition, the polygonal shape of the head section 14 enables mountedcomponents or plastic fastening elements (clips 34), given the provisionof suitable receptacles, to be able to act on the polygonal shape 22 inorder to permit anti-rotation locking or adjustment in the correctposition.

The stud 10 can generally be used universally. It may be provided withor without a pre-completed plastic part (for example welding of the stud10 to the workpiece, wherein the plastic fastening element is alreadypre-fitted on the stud 10, as is advantageous, for example, in underbodyfastening).

In this embodiment, care should possibly be taken to ensure that thepre-fitted plastic fastening element leaves at least part of thepolygonal shape 22 of the head section 20 free in order to still be ableto exert the test torque in the body-in-white phase.

Furthermore, the stud 10 can also be welded onto a workpiece 32 withoutpre-fitted plastic part, as described above. A plastic fastening elementsuch as a clip 34 can then be fastened thereto, for example in anassembly area.

The stud 10 is preferably welded on by arc welding with drawn arc. Inthe process, the annular surface 19 is set down on the workpiece 32. Anelectric pilot current is then switched on. The stud 10 is then liftedagain from the workpiece 32, in the course of which an arc is struck.After that, if need be a cleaning current is switched on (not absolutelynecessary). Finally, a welding current which is markedly higher than thepilot current is switched on, the energy being sufficient in order tofuse the front annular surface 19 and a corresponding mating surface onthe workpiece 32. Finally, the stud 10 is lowered again onto theworkpiece 32, in the course of which the molten pools fuse together. Thewelding current is then switched off. The complete molten poolsolidifies, and the stud 10 is integrally connected to the workpiece 32.

Although exemplary embodiments of the present invention have been shownand described, it will be appreciated by those skilled in the art thatchanges may be made to these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A weld stud for stud welding, comprising a shank, a flange axiallyadjoining the shank, the flange projects radially relative to the shankand defines a polygon shaped outer circumference; an annular sectionaxially adjoining the flange and including an axially facing andradially extending annular weld surface; and the annular section and theflange comprise a head section of uniform outside diameter throughout,and the polygonal shape of the flange extends over the annular sectionup to its axially facing annular weld surface.
 2. A weld stud accordingto claim 1, wherein the stud is made in one piece of metal, inparticular steel.
 3. A weld stud according to claim 1, wherein the studis produced by a cold forming process.
 4. A weld stud according to claim1, wherein the shank has a thread.
 5. A weld stud according to claim 1,wherein the polygonal shape is an octagonal shape.
 6. A weld studaccording to claim 1, wherein the head section defines an axial lengthand an outside diameter, and a ratio of the axial length of the headsection to the outside diameter of the head section is within the rangeof 1/7 to 3/4.
 7. A weld stud according to claim 6, wherein the flangedefines a second axial length, and the ratio of the second axial lengthof the flange to the axial length of the head section is within therange of 3/10 to 5/10.
 8. A weld stud according to claim 6, wherein theflange defines a second axial length, and the ratio of the second axiallength of the flange to the axial length of the head section is lessthan 5/10
 9. A welded assembly comprising: the workpiece defining athickness of less than 1 mm, and a stud welded to the workpiece and thestud includes: a shank, a flange axially adjoining the shank, the flangeprojects radially relative to the shank and defines a polygon shapedouter circumference; an annular section axially adjoining the flange andincluding an axially facing and radially extending annular weld surface;and the annular section and the flange comprise a head section ofuniform outside diameter throughout, and the polygonal shape of theflange extends over the annular section up to its axially facing annularweld surface.
 10. A weld stud according to claim 9, wherein theworkpiece thickness is less than 0.8 mm.
 11. A weld stud according toclaim 9, wherein the stud is produced by a cold forming process.
 12. Aweld stud according to claim 9, wherein the shank has a thread.
 13. Aweld stud according to claim 9, wherein the polygonal shape is anoctagonal shape.
 14. A weld stud according to claim 9, wherein the headsection defines an axial length and an outside diameter, and a ratio ofthe axial length of the head section to the outside diameter of the headsection is within the range of 1/7 to 3/4.
 15. A weld stud according toclaim 14, wherein the flange defines a second axial length and the ratioof the second axial length of the flange to the axial length of the headsection is within the range of 3/10 to 5/10.
 16. A method of welding aweld stud to a workpiece and of checking the strength of the weldedjoint, comprising the steps: providing a tool, a workpiece, and a weldstud, the weld stud comprising: a shank, a flange axially adjoining theshank, the flange projects radially relative to the shank and defines apolygon shaped outer circumference; an annular section axially adjoiningthe flange and including an axially facing and radially extendingannular weld surface; and the annular section and the flange comprise ahead section of uniform outside diameter throughout, and the polygonalshape of the flange extends over the annular section up to its axiallyfacing annular weld surface; welding the weld stud onto the workpiece,in particular by drawn-arc stud welding; and attaching the tool to thehead section of the stud and applying a predetermined torque to the weldstud in order to check the strength of the welded joint.
 17. A method ofwelding a weld stud to a workpiece and of checking the strength of thewelded joint according to the steps of claim 16, wherein the step ofwelding the stud is by drawn-arc stud welding.